IEC 63012:2019

IEC 63012 ®
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Unused modified or blended esters for electrotechnical
applications
Isolants liquides – Esters neufs modifiés ou mélangés pour applications
électrotechniques
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IEC 63012 ®
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Insulating liquids – Unused modified or blended esters for electrotechnical

applications
Isolants liquides – Esters neufs modifiés ou mélangés pour applications

électrotechniques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.040.10 ISBN 978-2-8322-6894-0

– 2 – IEC 63012:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 9
4 Classification . 10
4.1 General . 10
4.2 Fire performance classification . 10
4.3 Viscosity classification . 10
5 Properties, significance and test methods . 10
5.1 Physical properties . 10
5.1.1 Appearance . 10
5.1.2 Colour . 11
5.1.3 Viscosity . 11
5.1.4 Lubricity . 11
5.1.5 Thermal conductivity . 11
5.1.6 Thermal expansion coefficient . 11
5.1.7 Specific heat capacity . 11
5.1.8 Pour point . 11
5.1.9 Water content . 12
5.1.10 Water saturation . 12
5.1.11 Density . 12
5.1.12 Interfacial tension . 12
5.2 Electrical properties . 12
5.2.1 AC breakdown voltage . 12
5.2.2 Lightning impulse breakdown voltage . 12
5.2.3 Partial discharge inception voltage (PDIV) . 13
5.2.4 Dielectric dissipation factor (DDF) . 13
5.2.5 Relative permittivity (dielectric constant) . 13
5.2.6 DC resistivity . 13
5.2.7 Electrostatic charging tendency (ECT) . 13
5.3 Chemical properties . 13
5.3.1 Acidity . 13
5.3.2 Additive content . 13
5.3.3 Corrosive and potentially corrosive sulphur compounds . 13
5.3.4 Methanol content . 14
5.4 Properties related to long term performance . 14
5.4.1 Oxidation stability . 14
5.4.2 Operating temperature . 14
5.4.3 Material compatibility . 15
5.4.4 Stray gassing . 15
5.4.5 Gassing tendency . 15
5.5 Health, safety and environmental properties . 15
5.5.1 General . 15
5.5.2 Polychlorinated biphenyls (PCBs) . 15
5.5.3 Environmental toxicity . 15

5.5.4 Flash point and fire point . 15
5.5.5 Sustainability . 16
5.5.6 Biodegradation . 16
5.5.7 Disposal . 16
6 Minimum performance requirements . 16
7 Identification and general delivery requirements . 16
Annex A (informative) Miscibility and compatibility of liquids and retrofilling of

transformers . 19
Bibliography . 20

Table 1 – Required performance characteristics of modified or blended esters . 17
Table 2 – Optional performance characteristics of modified or blended esters . 18

– 4 – IEC 63012:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATING LIQUIDS – UNUSED MODIFIED OR BLENDED ESTERS
FOR ELECTROTECHNICAL APPLICATIONS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 63012 has been prepared by IEC Technical Committee 10: Fluids
for electrotechnical applications.
The text of this International Standard is based on the following documents:
FDIS Report on voting
10/1078/FDIS 10/1082/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 63012:2019 © IEC 2019
INTRODUCTION
Electrical insulation and heat transfer are essential functions of insulating liquids for
electrotechnical applications. Until recently, these liquids have been normally homogeneous,
selected from different categories, such as most common mineral oils or newer synthetic
esters, natural esters or silicone liquids. The continuous research for improvement of
performance characteristics of equipment drives an interest in exploring benefits from
combinations of liquids. Some known examples of desired improved characteristics include
optimized liquid cost, increased cooling performance, improved flash point, extended
insulation life or reduced environmental impacts.
Currently, international standards exist for specifically defined liquid categories (mineral oils,
synthetic esters, natural esters, silicone liquids). None of them cover chemically modified
natural ester liquids or blends of various esters. Moreover, the existing standards do not
cover synthetic esters whose characteristics may go beyond the limits defined in IEC 61099.
Some modified esters or their blends are already available as commercial products by liquid
suppliers. Examples are:
• Palm fatty acid ester with low viscosity of 5 mm /s at 40 °C and with flash point of 176 °C.
• Blend of triglycerides (50 %) and monoesters (50 %) with low viscosity of 17 mm /s at
40 °C and with flash point of 200 °C.
The number of sources for ester liquids or their blends is expected to grow over the coming
years. Such liquids need to be characterized to confirm suitability for the intended application
by the user. Performance characteristics of blends should not be solely assumed from
performance characteristics of their individual components. This document is to provide
minimum requirements on characterization of new compositions.
WARNING
This document sets performance criteria for unused modified/synthetized or blended esters
earmarked for electrical applications. This document does not purport to address all the safety
problems associated with their use. It is the responsibility of the user of this document to
establish appropriate health and safety practices and determine the applicability of regulatory
limitation prior to use.
Performance of some of the tests mentioned in this document could lead to a hazardous
situation. Attention is drawn to the relevant standard test method for guidance.
The disposal of liquids, chemicals and sample containers mentioned in this document should
be carried out in accordance with current local and national legislation with regards to the
impact on the environment. Every precaution should be taken to prevent the release of the
liquid into the environment.
INSULATING LIQUIDS – UNUSED MODIFIED OR BLENDED ESTERS
FOR ELECTROTECHNICAL APPLICATIONS

1 Scope
This document defines requirements for the characterization of unused modified esters or
blends of unused esters used as insulating liquids for electrotechnical applications. It does not
cover liquids that contain any proportion of used liquids.
The liquids covered by this document are intended mainly for transformer applications.
Unused modified/synthetized esters are derived from a natural or synthetic base, or are
blends of both. This document covers a variety of ester liquids not covered by other standards
specific to natural esters (IEC 62770) or synthetic esters (IEC 61099).
As it addresses various categories of liquids, this document also covers a wide range of
values for certain performance characteristics. An important property is viscosity, which can
affect the design and cooling performance of electrical equipment. A categorization is defined
based on the kinematic viscosity of the different liquids. The category of low viscosity ester
liquids is established.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60156, Insulating liquids – Determination of the breakdown voltage at power frequency –
Test method
IEC 60247, Insulating liquids – Measurement of relative permittivity, dielectric dissipation
factor (tan δ) and d.c. resistivity
IEC 60666, Detection and determination of specified additives in mineral insulating oils
IEC 60628, Gassing of insulating liquids under electrical stress and ionization
IEC 60814, Insulating liquids – Oil-impregnated paper and pressboard – Determination of
water by automatic coulometric Karl Fischer titration
IEC 60897, Methods for the determination of the lightning impulse breakdown voltage of
insulating liquids
IEC 61099:2010, Insulating liquids – Specifications for unused synthetic organic esters for
electrical purposes
IEC 61125, Insulating liquids – Test methods for oxidation stability – Test method for
evaluating the oxidation stability of insulating liquids in the delivered state
IEC TR 61294, Insulating liquids – Determination of the partial discharge inception voltage
(PDIV) – Test procedure
– 8 – IEC 63012:2019 © IEC 2019
IEC 61619, Insulating liquids – Contamination by polychlorinated biphenyls (PCBs) – Method
of determination by capillary column gas chromatography
IEC 61620, Insulating liquids – Determination of the dielectric dissipation factor by
measurement of the conductance and capacitance – Test method
IEC 62021-3, Insulating liquids – Determination of acidity – Part 3: Test methods for non-
mineral insulating oils
IEC 62535, Insulating liquids – Test method for detection of potentially corrosive sulphur in
used and unused insulating oil
IEC 62697-1, Test method for quantitative determination of corrosive sulfur compounds in
unused and used insulating liquids – Part 1: Test method for quantitative determination of
dibenzyldisulfide (DBDS)
IEC 62770, Fluids for electrotechnical applications – Unused natural esters for transformers
and similar electrical equipment
IEC 62961, Insulating liquids – Test methods for the determination of interfacial tension of
insulating liquids – Determination with the ring method
ISO 2049, Petroleum products – Determination of colour (ASTM scale)
ISO 2211, Liquid chemical products – Measurement of colour in Hazen units (platinum-cobalt
scale)
ISO 2592, Petroleum and related products – Determination of flash and fire points –
Cleveland open cup method
ISO 2719, Determination of flash point – Pensky-Martens closed cup method
ISO 3016, Petroleum products – Determination of pour point
ISO 3104, Petroleum products – Transparent and opaque liquids – Determination of kinematic
viscosity and calculation of dynamic viscosity
ISO 3675, Crude petroleum and liquid petroleum products – Laboratory determination of
density – Hydrometer method
ISO 12185, Crude petroleum and petroleum products – Determination of density – Oscillating
U-tube method
EN 14210, Surface active agents – Determination of interfacial tension of solutions of surface
active agents by the stirrup or ring method
ASTM D1275, Standard test method for corrosive sulphur in electrical insulating liquids
ASTM D1903, Standard practice for determining the coefficient of thermal expansion of
electrical insulating liquids of petroleum origin, and askarels
ASTM D3300, Standard test method for dielectric breakdown voltage of insulating oils of
petroleum origin under impulse conditions
ASTM D4172, Standard test method for wear preventive characteristics of lubricating fluid
(four-ball method)
ASTM D7150, Standard test method for the determination of gassing characteristics of
insulating liquids under thermal stress
ASTM D7896, Standard test method for thermal conductivity, thermal diffusivity and
volumetric heat capacity of engine coolants and related fluids by transient hot wire liquid
thermal conductivity method
ASTM E1269, Standard test method for determining specific heat capacity by differential
scanning calorimetry
DIN 51350-1, Testing of lubricants – Testing in the four-ball tester – Part 1: General working
principles
DIN 51350-2, Testing of lubricants – Testing in the four-ball tester – Part 2: Determination of
welding load of liquid lubricants
DIN 51350-3, Testing of lubricants – Testing in the four-ball tester – Part 3: Determination of
wearing characteristics of liquid lubricants
OECD 301-B, OECD Guidelines for the testing of chemicals – Section 3: Environmental fate
and behaviour – 301 Ready biodegradability – 301 B: CO Evolution test
OECD 301-C, OECD Guidelines for the testing of chemicals – Section 3: Environmental fate
and behaviour – 301 Ready biodegradability – 301 C: Modified MITI test
OECD 301-F, OECD Guidelines for the testing of chemicals – Section 3: Environmental fate
and behaviour – 301 Ready biodegradability – 301 F: Manometric respirometry test
U.S. Environmental Protection Agency, EPA 712-C-98-076, US EPA OPPTS Series 835: Fate,
transport and transformation test guidelines – Group C: Laboratory biological transformation
test guidelines – 835.3110 Ready biodegradability
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp/ui
3.1
unused insulating liquid
liquid as delivered by the supplier which has not been used in, or been in contact with
electrical equipment or other equipment not required for its manufacture, storage or transport
3.2
ester insulating liquid
insulating liquid consisting of fatty acid esters
Note 1 to entry: Fatty acid esters are commonly prepared from the reaction of alcohols and carboxylic acids or
found naturally in vegetable oils and fats.
3.3
modified ester insulating liquid
ester insulating liquid which has been made/synthesized or altered by chemical reaction

– 10 – IEC 63012:2019 © IEC 2019
Note 1 to entry: The chemical reaction could come about by means of organic chemistry processes, or
biochemical processes including enzymatic reactions.
Note 2 to entry: Modified ester insulating liquids can, for example, be composed of triglycerides, polyol esters,
fatty acid monoesters, fatty acid diesters or combinations thereof.
3.4
blended ester insulating liquid
homogeneous combination of unused natural, synthetic and/or modified esters that are
miscible
Note 1 to entry: The natural esters in this definition are those defined in IEC 62770, synthetic esters in this
definition are those defined in IEC 61099.
3.5
additive
chemical substance which is deliberately added to an insulating liquid in small proportion in
order to improve certain characteristics
4 Classification
4.1 General
As it addresses various compositions of insulating liquids, this document also covers a range
of values for certain performance characteristics when these are compared to other
recognized liquids with precisely defined performance characteristics. Therefore, the following
categorizations are established.
4.2 Fire performance classification
The insulating liquids are classified for fire performance according to IEC 61039.
4.3 Viscosity classification
Viscosity influences heat transfer and therefore the temperature rise of the equipment. The
lower the viscosity, the easier the liquid circulates leading to improved heat transfer.
Viscosity of natural esters and some synthetic esters is usually higher than that of mineral oil.
This requires special considerations at the equipment design stage and may affect
performance of equipment at low temperatures, too. Adjustment of modified or blended ester
composition allows for tailoring the viscosity and other properties to fit the equipment design
requirements.
Based on the viscosity, the liquids are classified as in Table 1. The category V1 refers to
esters of low viscosity, similar to mineral oils. The category V2 refers to esters of higher
viscosity than V1, but still lower than typical synthetic or natural esters. The category V3
refers to modified or blended esters that do not show low viscosity characteristics.
NOTE At the stage of development of this document, there are no commercial modified or blended esters with
viscosity category V3. This category makes provision for future technical developments.
5 Properties, significance and test methods
5.1 Physical properties
5.1.1 Appearance
A visual inspection of unused modified or blended esters (with light transmitted through
approximately 10 cm thickness of the liquid at ambient temperature) shall not indicate the
presence of visible contaminants, free water or suspended matter.

5.1.2 Colour
If required, colour shall be measured according to ISO 2211 (Hazen scale) or ISO 2049
(ASTM scale).
5.1.3 Viscosity
Kinematic viscosity shall be measured according to ISO 3104 and reported at 40 °C. The user
can request viscosity values in the range of temperatures 0 °C to 100 °C (with at least three
points: 0 °C, 40 °C and 100 °C).
NOTE Another suitable method for viscosity measurement is given in ASTM D7042.
It is beneficial to have the value of viscosity at temperatures below 0 °C to understand the
behaviour of the liquid in temperatures near the pour point, for example at −20 °C.
NOTE Viscosity at very low temperatures can be measured according to IEC 61868.
At low temperatures, the resulting higher viscosity of liquid is a critical factor for the cold start
of transformers with natural liquid circulation (no forced circulation and therefore possible
overheating at the hot spots) and negatively influences the speed of moving parts, such as in
power circuit breakers, switchgear, on-load tap changer mechanisms, pumps and regulators.
Lowest cold start energizing temperature (LCSET) requirements should be agreed upon
between supplier and purchaser.
5.1.4 Lubricity
If liquid is to be used in equipment with moving parts, for example switching equipment, tap
changers, the lubricity shall be measured. The test method shall be that given in ASTM D4172
or DIN 51350 (parts 1 through 3). In the case of ASTM D4172, the test parameters shall be:
load 392 N, rotation speed 1 200 r/min temperature 75 °C, duration 60 min.
5.1.5 Thermal conductivity
Thermal conductivity shall be measured in accordance with ASTM D7896 and the value shall
be given by the manufacturer.
NOTE Users can request that the thermal conductivity be measured at a range of temperatures, e.g. 0 °C to
100 °C (at least three points), for calculating the thermal performance of the equipment in different conditions.
5.1.6 Thermal expansion coefficient
Thermal expansion coefficient shall be measured in accordance with ASTM D1903 and the
value shall be reported by the manufacturer.
NOTE Users can request that the thermal expansion coefficient be measured at a range of temperatures, e.g.
0 °C to 100 °C (at least three points), for calculating the thermal performance of the equipment in different
conditions.
5.1.7 Specific heat capacity
Specific heat shall be measured in accordance with ASTM E1269 and the value shall be given
by the manufacturer.
NOTE Users can request that the specific heat capacity be measured at a range of temperatures, e.g. 0 °C to
100 °C (at least three points), for calculating the thermal performance of the equipment in different conditions.
5.1.8 Pour point
Pour point of insulating liquid is the lowest temperature at which the liquid is just sufficiently
fluid to flow at test conditions. Pour point shall be measured in accordance with ISO 3016.
Table 1 gives the requirement for a maximum pour point of −25 °C acceptable for modified or
blended esters. A lower value may be required by end users based on regional ambient

– 12 – IEC 63012:2019 © IEC 2019
conditions. It is recommended that the pour point should be minimum 10 K below the lowest
cold start energizing temperature (LCSET). LCSET requirements should be agreed upon
between supplier and purchaser.
Crystallization behaviour of modified or blended esters depends on time and temperature.
Crystals should not be present in the liquid at application temperature; precautions shall be
taken if liquid temperature inside the electrical device is lower than 0 °C. Below this
temperature, the thermal, mechanical and dielectric behaviour of the device with modified or
blended esters can be adversely affected.
NOTE For the evaluation of crystallization, a method is described in IEC 61099:2010, Annex A. The cloud point,
an indication of crystallization, can be measured according to the methods given in ISO 3015 or AOCS Cc 6-25.
5.1.9 Water content
The water content of modified or blended esters affects their dielectric properties. Water
content shall be measured in accordance with IEC 60814.
5.1.10 Water saturation
Water saturation is defined as a maximum amount of water that can be dissolved in the
insulating liquid at a specific temperature. If required, water saturation should be measured
and the value should be given by the manufacturer for a range of temperatures (e.g. 20 °C
to 100 °C). The test method shall be reported with test results.
NOTE For information refer to CIGRE Brochure 349 and CIGRE Brochure 741.
5.1.11 Density
Density of modified or blended esters shall be measured in accordance with ISO 12185 and
reported at 20 °C (reference method), but ISO 3675 is also acceptable. The test method shall
be reported.
NOTE 1 Another suitable method for density measurement is given in ASTM D7042.
NOTE 2 Users can request that the density be measured at a range of temperatures, e.g. 0 °C to 100 °C (at least
three points), for calculating the thermal performance of the equipment in different conditions.
5.1.12 Interfacial tension
The interfacial tension between insulating liquids and water provides a means of detecting
soluble polar contaminants and products of degradation. If requested, the following standards
shall be used for the determination of interfacial tension: IEC 62961 or EN 14210.
5.2 Electrical properties
5.2.1 AC breakdown voltage
Breakdown voltage of unused modified or blended esters shall be measured in accordance
with IEC 60156, which was developed for mineral oils. However, due to the high viscosity of
some modified or blended esters, the set-up time before application of the voltage and resting
time between voltage applications shall be extended as suggested in IEC 60156.
5.2.2 Lightning impulse breakdown voltage
If required, for characterization of the lightning impulse breakdown voltage of the liquid,
IEC 60897 shall be used. Alternatively, ASTM D3300 can be used. Similarly to the AC
breakdown voltage and due to the higher viscosity of some modified or blended esters, the
set-up time before application of the voltage and resting time between voltage applications
shall be extended as suggested in IEC 60156. The test method shall be reported.

5.2.3 Partial discharge inception voltage (PDIV)
If required, for the characterization of the PDIV of the liquid, IEC TR 61294 shall be used.
5.2.4 Dielectric dissipation factor (DDF)
DDF is a measure of dielectric losses caused by the liquid. A high DDF can indicate
contamination of the liquid with moisture, particles or soluble polar contaminants or poor
manufacturing quality. DDF shall be measured in accordance with IEC 60247 or IEC 61620 at
90 °C. The test method shall be reported. In case of dispute, IEC 60247 at 90 °C shall be
used.
NOTE Users can require that the DDF be measured at other temperatures.
5.2.5 Relative permittivity (dielectric constant)
Relative permittivity (dielectric constant) is the ratio of the amount of electric energy stored in
the liquid at an applied voltage, relative to that stored in a vacuum. It shall be measured in
accordance with IEC 60247 at 90 °C, and reported.
5.2.6 DC resistivity
If required, the DC resisitivity shall be measured in accordance with IEC 60247.
5.2.7 Electrostatic charging tendency (ECT)
The ECT of liquid is an important property for certain designs of transformers which have
liquid pumping rates that can give rise to the build-up of electrostatic charge. This charge can
result in energy discharge causing transformer failure.
A method to measure ECT is proposed by CIGRE Technical Brochure 170.
5.3 Chemical properties
5.3.1 Acidity
Acidity shall be measured in accordance with IEC 62021-3.
NOTE The acidity of unused ester liquids is typically higher than that of mineral oils.
5.3.2 Additive content
Additives include antioxidants, pour point depressants, electrostatic charging tendency
depressants, metal passivators or deactivators, antifoam agents, refining process improvers,
etc. The antioxidant additive slows down the oxidation of ester liquids and, in turn, the
formation of gels and acidity. One such antioxidant is phenolic 2,6-di-tert-butyl-p-cresol
(DBPC), also known as butylated hydroxytoluene (BHT), but others are also used. Detection
and measurement of defined antioxidant and other additives shall be in accordance with
IEC 60666 or other appropriate methods. Appropriate methods are normally those which have
published precision data where repeatability, reproducibility and limit of detection are known.
The function, chemical nature and concentrations of additives shall be declared.
The total concentration of additives shall be less than a weight fraction of 5 %.
5.3.3 Corrosive and potentially corrosive sulphur compounds
Corrosive and potentially corrosive compounds are detected by placing copper in contact with
insulating liquid under standardized conditions (IEC 62535 or ASTM D1275). Known corrosive

– 14 – IEC 63012:2019 © IEC 2019
or potentially corrosive sulphur compounds such as dibenzyl disulphide (DBDS) shall not be
present above the detection limit (IEC 62697-1).
Under the influence of heat, sulphur containing molecules may decompose and react with
metal surfaces to form metal sulphide layers. Switching equipment often features silver-plated
contacts, which are very sensitive to reactions with certain sulphur compounds. The contact
resistance may increase or silver-sulphide layers may flake off, promoting flashovers. The test
method in DIN 51353 is an appropriate method to detect reactions of corrosive sulphur with
silver.
NOTE 1 Corrosive sulphur compounds are not naturally present in ester liquids in general. The test, however, can
verify that additives are non-corrosive and that cross-contamination with potentially corrosive liquids has not
occurred.
NOTE 2 Another suitable method to assess potential corrosivity is described in IEC TR 62697-2.
5.3.4 Methanol content
The standard test method for measuring methanol content (IEC 63025 series ) is at the
development stage.
5.4 Properties related to long term performance
5.4.1 Oxidation stability
For the evaluation of oxidation stability performance, IEC 61125 shall be used. The resistance
to oxidation is evaluated based on the amount of sludge, total acidity and dielectric dissipation
factor or from the time it takes to develop a given amount of volatile acidity (induction period).
Additionally, for modified or blended esters the viscosity change during the oxidation stability
test shall be measured.
For liquids intended for use in sealed systems, IEC 61125 shall be used with 48 h test
duration, and minimum performance requirement limits are based on IEC 62770. If requested,
the amount of sludge shall be reported.
For liquids intended for use in free breathing systems or other applications, IEC 61125 shall
be used with 164 h test duration, and minimum performance requirement limits are based on
IEC 61099. If requested, the DDF and viscosity change shall be reported.
NOTE Oxidation stability according to IEC 61125 at 500 h is an optional extra stability test. No performance limits
are defined in this document.
5.4.2 Operating temperature
IEC 60076-14 provides guidance on the maximum acceptable temperatures for operation of
ester liquids. Those are based on typical K-class natural esters and synthetic esters in
accordance with IEC 62770 and IEC 61099, respectively. While the temperature performance
of the modified or blended esters could be expected to be better than that of mineral oil due to
the nature of ester liquids, guidance on applicable temperatures in IEC 60076-14 may not
apply to the liquids under the scope of this document. Individual evaluation of liquid
performance shall be made to establish acceptable limits for the operating temperature.
Currently, there are no standard IEC methods for this evaluation. As a minimum, the side-by-
side comparison of liquid performance at selected temperatures shall be made against the
natural or synthetic esters according to IEC 62770 or IEC 61099, respectively.
___________
The IEC 63025 series is under consideration. Stage at the time of publication, IEC ACD 63025-1:2019 and
IEC ACD 63025-2:2019.
5.4.3 Material compatibility
Compatibility of the dielectric liquid with materials it may come into contact with shall be
determined under the standard operating conditions of the application. This refers to the list of
materials, operating temperatures range, free breathing versus sealed system, etc.
There is no current ISO or IEC test method for material compatibility evaluation. However,
there are references for material compatibility, such as ASTM D471, ASTM D4289,
ASTM D3455. They could be used as guides for defining the compatibility test procedures.
NOTE See also Annex A.
5.4.4 Stray gassing
Gases such as hydrogen, ethane and carbon oxides can be generated from ester-based
liquids under normal operating conditions in the absence of thermal or electrical fault. These
gases are referred to as 'stray gases'. If requested, stray gassing characteristics of liquids
shall be determined in accordance with ASTM D7150.
NOTE A new test method is under development and will be included in the next edition of IEC 60296, under
preparation.
5.4.5 Gassing tendency
By definition, the gassing tendency is the ability of the liquid to absorb or evolve gases
(hydrogen only) under electrical corona or partial discharge. The measurement shall be made
in accordance with method A in IEC 60628.
5.5 Health, safety and environmental properties
5.5.1 General
These are the properties that are related to safe handling of modified or blended e
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